Electro-optical devices are indispensable in this age of high-speed optical, and digital communications. These applications require high bandwidth, low skew and cross talk, and high interconnect density. There is an on-going effort to develop micro- and submicrometer size optical components. A majority of such components are built using existing technologies. But these components are not switchable which is essential for reprogrammable interconnects, angle multiplexers, data storage, and dynamically variable focal length devices.
With the advancements in computing and communications technology, there is a growing and critical need for real-time reconfigurable optical elements such as fast optical switches, diffractive gratings, and microlens arrays for use in high-density optical interconnections, beam steering, and modulating devices. The ability to electrically switch/control the action of these devices is a key requirement. Until now, various technologies have been used in attempts to build such devices based on liquid crystals, polymers, and solid state materials. For example, passive elements have been built using surface relief structures. Methods to build active microlens arrays include (i) a combination of passive solid state planar optical components and a liquid crystal (LC) modulator, and (ii) gradient refractive index profile (GRI) of liquid crystal switched with an axially symmetric electric field generated with specially designed electrode patterns. Switchable optical gratings have been made using polymer dispersion of liquid crystal, known as the PDLC technology. Their performance is marred by factors such as high light scattering due to their internal structure and the need for high operating voltages. Furthermore, the size of droplets in PDLCs, which is in the several micron range with high polydispersity, puts a lower limit on the size of these microstructures. A second approach uses alternatingly aligned linear domains or lines of LC. These devices are built with cumbersome processes. Furthermore, this method cannot be used for two-dimensional arrays which are necessary for high interconnect density.
In order to build an optical modulator of a well defined shape of liquid crystal volume, specific methods have been proposed. An electrooptical medium may be obtained by er, confining liquid crystal within polymer walls using UV exposure with a photo mask. However, in this method, the phase separation is promoted by UV exposure only in the UV exposed region. Since the liquid crystal rich structure is formed only in non-UV exposed region, the structure is non-uniform. An electro-optical device can also be made using liquid crystal confined by polymer walls using UV exposure while applying an electric field (Appl. Phys. Lett. V72, p2253 (1998)). However, in this case, polymer walls are produced by applying high (10 V μm) electric field to separate the LC from the polymer, with the polymer walls then shaped by polymerization initiated by UV exposure. The LC regions in the direction perpendicular to the cell cannot be controlled limiting its utility. Alternatively, a display medium may be obtained by confining liquid crystal inside microdroplets. In this method, the liquid crystal is confined in microdroplets, and a relatively high voltage is used to change the orientation of the liquid crystal. However, it is not possible to control the shape of the microdroplets and LC director configuration inside them.
Clearly, there is need for lowest, high-speed, and high-performance electro-optical devices which can be built with relative ease and operated at low voltages. A promising technology is disclosed in U.S. Pat. No. 5,949,508, which is in incorporated herein by reference. This patent teaches forming phase separated composite films (PSCOF) that result in parallel layers of pure LC and polymer and with a desired orientation of the LC optic axis. An electric field may be used to control the optical axis to control their performance. PSCOF structures have highly desirable properties not previously observed in devices prepared by other methods. Such devices can be prepared with rigid as well as flexible substrates with excellent tolerance to mechanical deformations.
Based upon the foregoing, it is evident that there is a need in the art for a liquid crystal microstructure precisely defined and bounded by a polymeric material. There is also a need for such a microstructure to be electrically controllable and contained within a stable package for use in high-density electro-optical devices.